This invention relates to welding, and more particularly to an apparatus and method for butt welding a joint between two closely spaced vertical members.
In the electroslag welding of a joint between two closely spaced vertical members, e.g. steel plates, with consumable electrodes, a plurality of strongbacks are secured across the joint lengthwise thereof to maintain the joint opening constant during the welding of the joint. A pair of watercooled weld retaining shoes is then wedged between said strongbacks and said plates in registry on each side of the joint at the lower end thereof, one shoe of each pair being disposed directly above the other shoe. A consumable electrode guide tube, through which a weld wire is fed, is secured to the plates at the upper end thereof, said guide tube and wire extending to a point approximately at the bottom of the joint. Current is then supplied to the top of the guide tube resulting in a short circuit at the bottom of the joint between the end of the weld wire and the steel plates. A semiconductor granular flux is then added to the bottom of the joint, said flux becoming molten as a result of the heat produced by the short circuit. The molten flux covers the weld metal deposited in the joint as a result of the weld wire melting.
Up to this point, the process would be considered to be submerged arc welding. However, the welding mode changes to electroslag when the molten flux becomes hot enough to melt the constantly feeding weld wire, resulting in the termination of the arc between the end of the wire and the metal forming the joint.
As the weld metal solidifies and fills the joint, the molten flux, disposed on top of the rising weld, steadily consumes the guide tube as well as the constantly feeding wire. By capillary action and magnetic attraction, the melt, consisting of the melted portions of the wire and consumable guide tube, is attracted to the edges of the steel plates forming the joint and fuses therewith.
After the weld metal has solidified adjacent the lower shoes, and while the weld metal is being deposited in the joint adjacent the upper shoes, the lower shoes are "leap-frogged" over the upper shoes whereby one set of shoes is always disposed contiguous to liquid weld metal as the weld progresses upwardly along the joint.
While the foregoing method of welding vertical joints has been successful for relatively short joints, e.g. 3 meters or less, this method has been less than satisfactory for longer joints. This is due to high currents, as well as to the large voltage drop across the guide tube from the top to the bottom thereof during the initiation of the weld. The high currents cause the temperature of the guide tube to increase, thereby expanding the welding wire and restricting the flow thereof through the guide tube. The large voltage drop causes the voltage at the pool of weld metal to be too low for optimum welding to occur.
It is an object of this invention to provide a method and apparatus for electroslag welding a long joint between vertical members with consumable electrodes whereby the magnitudes of the voltage drop across, and the current through, the guide tube are limited to tolerable values.